This invention relates in general to gas-fired radiant burners of the infrared type, and in particular to a radiant burner having a heating element constituted by a boardlike fiber refractory material, commonly referred to as a matrix, that is porous to a combustible gas mixture forced through it from one side for incandescent burning at the other side. A supplier of a suitable refractory material of the subject type is Johns-Manville Corporation of Denver, Co., U.S.A. marketing such material under the trade names "Cera Form" and "Fiberchrome."
U.S. Pat. No. 3,785,763, assigned to the assignee of the present invention, illustrates an early design for a burner of the subject type wherein the open end of a sheet metal box is closed by the boardlike refractory material constituting the heating element or matrix. A combustible gas mixture fed into the box is exhausted through the porous matrix and burned at its exposed outside surface.
In operating this type of burner, it was found that high temperature gas by-products generated by the burning at the matrix surface flowed from around the edge of the matrix against the adjacent portions of the sheet metal box. Uneven heating of such adjacent portions caused severe thermal expansion and contraction of burner elements, resulting in mechanical failure of the sheet metal box or the heating element, or both. This thermal expansion and contraction problem became particularly acute where a burner of the subject type was faced downwardly to, for example, dry a textile fabric web traveling beneath it. Gas by-products would flow upwardly by convection and envelop the sheet metal box, heating portions of it to very high differential temperatures and creating severe thermal stresses in the burner.
A solution to such a problem is proposed by U.S. Pat. No. 4,035,132, which uses a stream of non-combustible cooling air about the periphery of the matrix to shield portions of the sheet metal box from the combusted gas by-products. A burner of the type illustrated by this patent is more complex and costly than a non-air cooled burner of the type illustrated by the heretofore discussed U.S. Pat. No. 3,785,763. It requires a plenum for the air and a plenum for the combustion mixture.
The object of the present invention is to provide a non-air cooled burner that operates satisfactorily in spite of the thermal stress problems noted above.